The Study On Physical Properties Of Transition Metal Fluorides

Transition metal fluorides have complex and diverse crystal structures accompanied by abundant physical properties such as multiferroicity,photoluminescence,and electrochemical properties.These materials are used in information storage,energy capture,and spintronics.There are many potential applications.The bottleneck in the development of perovskite oxide single-phase multiferroic materials is the contradictory in requirements of ferroelectricity and magnetism for d-orbital electron filling of 3d transition metal ions.However,in fluoride,F element has high electronegativity,making F and transition metal ions form ionic bonds,thereby breaking the d⁰ criterion in the perovskite oxide and achieving single-phase multiferroicity.In terms of energy storage,supercapacitors are interposed between conventional capacitors and batteries,and have special performance in energy supply,mainly relying on electrochemical adsorption/desorption effects or redox reactions to store electrical energy,and this energy storage process is highly reversible.Among them,the electrode material is an important factor affecting the energy storage effect of the supercapacitor.Many transition metal fluorides meet the basic conditions required for electrochemical electrode materials:quasi-two-dimensional structures can provide a large specific surface area,and transition metal ions can serve as a carrier for redox reactions.In the first chapter,the classification,preparation methods and physical properties of transition metal fluorides are first introduced.Secondly,a brief introduction to supercapacitors is given,including the types,principles,research status of supercapacitors,and the use of electrode materials and electrolytes.In the second chapter,the experimental preparation methods of the materials studied in this paper are introduced.The materials were fabricated by chemical deposition method and solid state reaction method.Then,the X-ray diffraction crystal structure analysis technology,scanning electron microscope SEM,ferroelectric analyzer,magnetic measurement,X-ray photoelectron spectrum experimental principle used in the experimental researches are described in detail.In the third chapter,pure phase KCoF₃ powder samples were prepared by chemical deposition method.The sample particles were small and had a large specific surface area.The variable-valent metal Co in the sample can also meet the redox reaction conditions required in supercapacitors.Therefore,we used KCoF₃ powder for the electrode material of supercapacitor.In the standard three-electrode system using 6 M KOH electrolyte,electrochemical measurements showed significant capacitance behavior and Faraday redox reaction.The KCoF₃ electrode exhibits excellent specific capacitance,and has excellent cycle life,good energy storage performance and excellent cycle life,making the transition metal fluoride KCoF₃ an active material for supercapacitors.In the fourth chapter,the solid state reaction method was used to prepare Sr₃Fe₂F₁₂sample.The pure phase of Sr₃Fe₂F₁₂ sample was proved by XRD,XPS,EDS structural and elemental characterizations.The sample was observed by SEM to have a smooth surface morphology.Further,the ferroelectricity of the sample was tested by a ferroelectric tester,and the observed hysteresis loop was not saturated due to the large leakage current.The FC and ZFC M-H curves of Sr₃Fe₂F₁₂ samples were tested by SQUID.It was found that there were magnetic phase transitions at T=47 K and T=29K.Further measurement of the hysteresis loop at low temperature indicated that Sr₃Fe₂F₁₂ had weak ferromagnetism at low temperature.The experiments confirmed that the sample has good multiferroic properties.